Systemic sclerosis (SSc) is a serious disease of unknown cause characterized by excessive accumulation of collagen and other connective tissue components in the skin and internal organs. The mechanisms responsible for such accumulation are not known. An animal model to study the molecular mechanisms of SSc would be extremely useful. We have been breeding a new mutant mouse known as the tight skin 2 or the Tsk-2 mouse. This mouse appears to be an excellent new model for SSc. In preliminary work, we have shown that the Tsk-2 mouse displays increased thickness and decreased pliability of the skin. Histologic examination shows-marked thickening of the dermis and excessive accumulation of dermal collagen. In biochemical studies, we found that collagen synthesis was increased 6 fold in Tsk-2 mouse skin. When RNA levels in skin were measured, type I collagen transcripts were also shown to be markedly elevated in the Tsk-2 mouse. These preliminary results demonstrate that the Tsk-2 mutant mouse appears to display connective tissue abnormalities which resemble those present in the skin of patients with SSc. With the discovery of the unique Tsk-2 mouse mutation, we now have another mouse model displaying connective tissue abnormalities similar to those found in SSc patients. The fact that two unique genetic mutations (Tsk-1 & Tsk-2) on separate chromosomes lead to similar phenotypic and molecular changes affecting the connective tissue is extremely important. It allows us a second avenue of approach to understanding the mechanisms controlling collagen gene expression at the molecular level and it greatly increases our chances of eventually finding more suitable treatment for SSc. In this application, we propose to characterize the connective tissue abnormalities present in the Tsk-2 mouse. Histopathologic studies will be performed on skin and internal organs and the results compared to those from Tsk-1 mice. Emphasis will be placed o the study of regulation of collagen synthesis in cultured fibroblasts applying state of the art biochemical methods and recombinant DNA techniques. We will identify the regulatory defect in the Tsk-2 mouse by mapping pertinent regions of the type I procollagen gene by transient transfections of intact and deleted putative regulatory sequences of the promoter. Because of the likely importance of the Tsk-2 gene in the regulation of collagen gene expression, we will identify the location of and begin the process of cloning the Tsk-2 gene employing intersubspecific backcross studies and chromosome walking. It is expected that the knowledge gained from these studies will bee of direct relevance to the understanding of the pathogenesis of the excessive collagen deposition characteristic of SSc and will provide a more rational approach to develop possible modes of therapy for this incurable and devastating disease.